1. Field of the Invention
The present invention relates generally to semiconductor devices with metal conductive traces. The present invention also relates to the use of metal oxide, especially copper oxide, to cover or mask selected portions of conductive patterns in semiconductor devices. The present invention also relates to methods of making semiconductor devices, and to methods of making electrical conductor systems for use in semiconductor devices.
2. Discussion of the Related Art
U.S. Pat. No. 5,756,380 (Berg et al.) describes a method of making a semiconductor device with conductive copper traces. The copper traces are patterned on an organic substrate, and then a resist solder mask is formed on the traces. The resist mask covers everything but certain contact portions of the traces. The exposed contact portions are gold plated to prevent oxidation, and then solder balls are attached to the respective gold plates. The resist mask prevents solder from flowing between the contact portions or down the copper traces.
There are several disadvantages associated with resist solder masks of the type shown in the Berg et al. patent. In particular, extra processing steps are required to coat the resist material onto the device and strip off the residual material. In addition, the resist material may interfere with the adhesion of the chip to the rest of the device. In addition, delamination of the resist mask may cause quality control problems. Such delamination is exhibited in preconditioned reflow tests (PRT) or xe2x80x9cpopcornxe2x80x9d tests. For these and other reasons, it would be advantageous to make semiconductor devices without resist solder masks of the type shown in the Berg et al. patent.
The disadvantages of the prior art are overcome to a great extent by the present invention. The present invention relates to a semiconductor device that has metal traces for connecting active elements to an external device, and insulating layers formed of metal oxide on the traces. The active elements may be, for example, conductors on the active surface of a semiconductor die (or chip). The external device may be, for example, a memory device or an input/output device.
According to a preferred embodiment of the invention, the semiconductor device does not have a resist solder mask. An advantage of the invention is that it eliminates the need for a resist solder mask. By not using a resist solder mask, the disadvantages mentioned above may be avoided.
In one aspect of the invention, conductive metal traces are covered by insulating layers of cupric oxide (CuO), also known as xe2x80x9cblack oxide.xe2x80x9d The present invention should not be limited to the preferred embodiment, however. Other metal oxides such as cuprous oxide (Cu2O), aluminum oxide, and the like, may also be used. Gold may be used to prevent oxidation of the portions of the copper traces that are not intended to be covered by metal oxide.
In another aspect of the invention, copper traces are partially covered by black oxide and used to provide electrical connections to a ball grid array (BGA) or fine ball grid array (FBGA). The black oxide prevents solder from adhering to the traces except where desired.
Black oxide may also be used to promote adhesion between the die and the substrate. In a preferred embodiment of the invention, all of the black oxide layers in a particular device are formed at the same time, and all such layers have essentially the same amount of surface roughness appropriate for obtaining the desired adhesion.
The black oxide layers preferably do not cover the entire surfaces of the semiconductor device. The black oxide layers grow only on the surfaces of the copper traces. Consequently, the dimensions of the finished device may be minimized.
The present invention also relates to a packaged semiconductor device that has a semiconductor die, copper traces for connecting the die to an external device, and copper oxide layered on the copper traces. The semiconductor die may be encapsulated in resin. The traces may be electrically connected to a solder ball grid array.
The present invention also relates to an electrical conductor system for use in a semiconductor device. The system has metal traces for connecting the semiconductor device to an external device, and metal oxide located on and masking portions of the metal traces.
The present invention also relates to a method of making a semiconductor device. The method includes the following steps: forming copper conductors on a substrate; growing copper oxide on the copper conductors; removing the copper oxide from portions of the conductors; and attaching conductive metal (e.g., gold plate and solder balls) to the portions of the conductors where the oxide is removed.
The present invention also relates to a method of making a conductor system, including the following steps: forming metal traces on a substrate (e.g., an organic substrate or a semiconductor die); forming cupric oxide on the metal traces; and attaching conductive metal to the traces (e.g., by depositing gold on exposed portions of the traces).
These and other features and advantages will become apparent from the following detailed description of preferred embodiments of the invention.